The present invention relates to a fuel cell system and a method of controlling the same, and more particularly, to a fuel cell control system of a polymer electrolyte type and a method of controlling a fuel cell of the polymer electrolyte type.
In recent years, considerable research and development work has been undertaken to commercially apply a fuel cell of polymer electrolyte membrane type, which has a high power density and which can be operated at low temperature, as an electric power generation system in a motor vehicle.
Such a fuel cell of the polymer electrolyte membrane is usually constructed of a polymer electrolyte membrane, an anode joined to one side of the membrane, and a cathode joined to the other side of the membrane to provide a joined structure, which is sandwiched between separators.
In a fuel cell system including a plurality of fuel cells of polymer electrolyte membrane type as a stack, fuel gas and air are usually humidified by a humidifier for preventing the polymer electrolyte membrane from being dried such that the polymer electrolyte membrane is kept in a suitably wet state throughout electric power generation.
In such a fuel cell system, however, a usual practice normally done in usual operation of the stack has been adapted to start up the stack, even when the fuel cell system is left in a non-use state for a long time period and the polymer electrolyte membrane remains in an excessively dry state.
For this reason, humidification of the polymer electrolyte membrane to a sufficiently wet state needs a preliminary longer operating time to some extent, with a resultant difficulty in taking out electric power output from the stack in a stable fashion or an undesirable system failure owing to rapid voltage drop caused when a large amount of electric power output is required.
The present invention has been made in view of the above-described studies and has an object to provide a fuel cell system and a method controlling the same which can achieve a substantially optimum start-up control even when a fuel cell system of a polymer electrolyte type remains in a dry state.
A fuel cell system of the present invention is provided with: a humidifier humidifying fuel gas and air; a stack producing electric power by reacting the fuel gas humidified by the humidifier and the air humidified by the humidifier, including a plurality of fuel cells and fixed for free movement in a stacked direction thereof, each of the plurality of fuel cells having a polymer electrolyte membrane; a displacement sensor detecting a displacement value in length of the stack in the stacked direction; a temperature sensor detecting a temperature of the stack; and a controller discriminating whether the polymer electrolyte membrane is in a dry state in response to the displacement value of the stack detected by the displacement sensor and the temperature of the stack detected by the temperature sensor and controlling the humidifier, when the polymer electrolyte membrane is discriminated as in a dry state at a start of operation of the stack, to cause the polymer electrolyte membrane to be brought into a wet state.
In other words, a fuel cell system of the present invention is provided with: humidifying means humidifying fuel gas and air; a stack producing electric power by reacting the fuel gas humidified by the humidifying means and the air humidified by the humidifying means, including a plurality of fuel cells and fixed for free movement in a stacked direction thereof, each of the plurality of fuel cells having a polymer electrolyte membrane; displacement detecting means detecting a displacement value in length of the stack in the stacked direction; temperature detecting means detecting a temperature of the stack; and controlling means discriminating whether the polymer electrolyte membrane is in a dry state in response to the displacement value of the stack detected by the displacement detecting means and the temperature of the stack detected by the temperature detecting means and controlling the humidifying means, when the polymer electrolyte membrane is discriminated as in a dry state at a start of operation of the stack, to cause the polymer electrolyte membrane to be brought into a wet state.
Besides, a method of controlling a fuel cell system is applied to a system provided with a humidifier humidifying fuel gas and air, and a stack producing electric power by reacting the fuel gas humidified by the humidifier and the air humidified by the humidifier, including a plurality of fuel cells and fixed for free movement in a stacked direction thereof, each of the plurality of fuel cells having a polymer electrolyte membrane. The method detects a displacement value in length of the stack in the stacked direction and a temperature of the stack, discriminates whether the polymer electrolyte membrane is in a dry state in response to the displacement value of the stack detected by the displacement sensor and the temperature of the stack detected by the temperature sensor, and controls the humidifier, when the polymer electrolyte membrane is discriminated as in a dry state at a start of operation of the stack, to cause the polymer electrolyte membrane to be brought into a wet state.
Other and further features, advantages, and benefits of the present invention will become more apparent from the following description taken in conjunction with the following drawings.